# US 8,572,517 B2 · System and method for modifying a data set of a photomask

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- Number: US 8,572,517 B2
- Document ID: US8572517B2
- Status: Granted
- Kind: B2
- Application number: 12/136,277
- Filed: 2008-06-10
- Published: 2009-12-10
- Granted: 2013-10-29
- Earliest claimed: 2008-06-10
- Assignees: Cadence Design Systems, Inc.
- Applicants: Dipankar Pramanik; Michiel Victor Paul Kruger; Roy V. Prasad; Abdurrahman Sezginer
- Inventors: Dipankar Pramanik; Michiel Victor Paul Kruger; Roy V. Prasad; Abdurrahman Sezginer
- Web page: https://patentgrep.com/patent/US8572517B2

## CPC

- G06F 30/398: Design verification or optimisation, e.g. using design rule check [DRC], layout versus schematics [LVS] or finite element methods [FEM] (optical proximity correction [OPC] design processes G03F1/36)
- G03F 1/36: Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes
- G06F 30/00: Computer-aided design [CAD]
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

The present invention provides a method for compensating infidelities of a process that transfers a pattern to a layer of an integrated circuit, by minimizing, with respect to a photomask pattern, a cost function that quantifies the deviation between designed and simulated values of circuit parameters of the pattern formed on a semiconductor wafer.

## Claims

### Claim 1

A method for optical compensation comprising:
using a computer system to create a simulated circuit pattern using a lithography process, wherein the lithography process uses a photomask defined by a data set having a plurality of polygons that define patterns on the photomask;
calculating a cost function based on an electrical parameter of the simulated circuit pattern, wherein the cost function comprises terms defined by at least one of:
(a) a sum of squares of normalized differences between simulated and designed values of electrical parameters for a multitude of circuit components,
(b) an amount by which the simulated value of the electrical parameter exceeds a maximum allowable value,
(c) an amount by which the simulated value of the electrical parameter falls below a minimum allowable value,
(d) the difference of simulated values of a first and a second electrical parameter of a simulated circuit pattern,
(e) a change in the simulated value of the electrical parameter in response to a change in a condition of the lithography process, and
(f) a restricted simulated value of the electrical parameter that is not larger than a maximum allowable value or not smaller than a minimum allowable value,
and wherein the electrical parameter describes an electrical operational characteristic of the simulated circuit pattern; and
adjusting the polygons based on the calculated cost function in order to reduce the value of the cost function.

### Claim 2 (depends on 1)

The method of claim 1, wherein adjusting the polygons comprises at least one of: segmenting an edge of a polygon, altering a polygon by moving a segment of its edge, moving a polygon, adding a polygon to the data set, and removing a polygon from the data set.

### Claim 3 (depends on 1)

The method of claim 1, wherein the electrical parameter comprises one or more parameters from the group consisting of saturation current, leakage current, threshold voltage, gain, resistance, capacitance, and inductance.

### Claim 4 (depends on 1)

The method of claim 1, wherein calculating the cost function further comprises using geometric variables derived from comparing the simulated circuit pattern with a target circuit pattern.

### Claim 5 (depends on 1)

The method of claim 1, further comprising adjusting distribution or polarization variables of the illumination in a pupil of an optical projector in a way to reduce the value of the cost function.

### Claim 6 (depends on 1)

The method of claim 1, wherein the method is performed using a computer program product having computer readable program code functions embedded in a non-transitory computer useable medium.

### Claim 7

A computer system configured for optical compensation, comprising:
a processor;
a memory connected to the processor; and
a computer-readable medium having instructions embedded therein, the instructions configured to cause the processor to perform the operations of:
creating a simulated circuit pattern using a lithography process, wherein the lithography process uses a photomask defined by a data set having a plurality of polygons that define patterns on the photomask;
calculating a cost function based on an electrical parameter of the simulated circuit pattern, wherein the cost function comprises terms defined by at least one of:
(a) a sum of squares of normalized differences between simulated and designed values of electrical parameters for a multitude of circuit components,
(b) an amount by which the simulated value of the electrical parameter exceeds a maximum permissible value,
(c) an amount by which the simulated value of the electrical parameter falls below a minimum allowable value,
(d) the difference of simulated values of a first and a second electrical parameter of a simulated circuit pattern,
(e) a change in the simulated value of the electrical parameter in response to a change in a condition of the lithography process, and
(f) a restricted simulated value of the electrical parameter that is not larger than a maximum allowable value or not smaller than a minimum allowable value,
and wherein the electrical parameter describes an electrical operational characteristic of the simulated circuit pattern; and
adjusting the polygons based on the calculated cost function in order to reduce the value of the cost function.

### Claim 8 (depends on 7)

The system of claim 7, wherein adjusting the polygons comprises at least one of: segmenting an edge of a polygon, altering a polygon by moving a segment of its edge, moving a polygon, adding a polygon to the data set, and removing a polygon from the data set.

### Claim 9 (depends on 7)

The system of claim 7, wherein the electrical parameter comprises one or more parameters from the group consisting of saturation current, leakage current, threshold voltage, gain, resistance, capacitance, and inductance.

### Claim 10 (depends on 7)

The system of claim 7, wherein calculating the cost function further comprises using geometric variables derived from comparing the simulated circuit pattern with a target circuit pattern.

### Claim 11 (depends on 7)

The system of claim 7, wherein the instructions are further configured to cause the processor to perform the operation of adjusting distribution or polarization variables of the illumination in a pupil of an optical projector in a way to reduce the value of the cost function.